Compare your cat's weight with the documented limit for the exact component it will use, as well as any stated limit for the complete tree. For example, Amber Rise lists a maximum of 15 kg per tier. Its separate 24 kg product weight describes the furniture itself and is not a carrying capacity. Do not add individual tier ratings together to invent a total rating for several cats.
If two cats may share a bed or climb at the same time, the manufacturer's guidance must cover that intended use. Ask for clarification where a listing does not distinguish one occupant, one platform and the complete assembly. Keep usable bed size and the route between levels in the comparison: a suitable weight figure does not make a cramped perch spacious. For a growing kitten, review its weight and dimensions as it develops rather than treating today's match as a lifetime guarantee. Assemble, stabilise and maintain the furniture according to its supplied instructions, because a published capacity does not replace correct installation.
For product comparisons alongside this advice, see Amber Rise and Ultimate PawHouse. The details below explain their sizes and uses.
Further reading: giantpaws.co.uk.
Amber Rise
Ultimate PawHouse